Quantum Science and Engineering at Cornell

‘Two-for-one’ fission aims to improve solar cell efficiency

Singlet fission occurs when an organic molecule absorbs one photon of light, then splits that light’s energy in two – a doubling effect that has the potential to improve the light-harvesting efficiency in solar cells, assuming the generated electrons can be properly harvested.

A Cornell-led team used ultrafast laser spectroscopy to scrutinize a key intermediate state during the fission process, called the triplet-pair state, and found that in certain molecules the intermediate can be directly generated by using a strikingly simple technique – in effect, singlet fission without the singlet.

The team’s paper, “Coherent Photoexcitation of Entangled Triplet Pair States,” published June 19 in Nature Chemistry.

Read the full story in the Cornell Chronicle.

Ultrasound experiment identifies new superconductor

With pulses of sound through tiny speakers, Cornell physics researchers have clarified the basic nature of a new superconductor. 

In an experiment, Brad Ramshaw, associate professor of physics in the College of Arts and Sciences (A&S) and colleagues used ultrasound to gather direct evidence that uranium ditelluride has a single-component superconducting order parameter, ruling out a more exotic type of superconductor that would have been exciting news for quantum computing. But setting a baseline of data for the material’s intrinsic superconductivity still leaves the door open for discovering additional complex possibilities through further study.

Read the full story in the Cornell Chronicle.

Semiconductor defects could boost quantum technology

In diamonds (and other semiconducting materials), defects are a quantum sensor’s best friend. That’s because defects, essentially a jostled arrangement of atoms, sometimes contain electrons with an angular momentum, or spin, that can store and process information. This “spin degree of freedom” can be harnessed for a range of purposes, such as sensing magnetic fields or making a quantum network.

Researchers led by Greg Fuchs, Ph.D. ’07, professor of applied and engineering physics in Cornell Engineering, went searching for such a spin in the popular semiconductor gallium nitride and found it, surprisingly, in two distinct species of defect, one of which can be manipulated for future quantum applications.

The group’s paper, “Room Temperature Optically Detected Magnetic Resonance of Single Spins in GaN,” published Feb. 12 in Nature Materials. The lead author is doctoral student Jialun Luo.

Read the full story in the Cornell Chronicle.